1245 Bernhard W. Schwaighofer1 2 Terry T. Tanaka3 Michael V. Klein1 David J. Sartons1 Donald Resnick4 Received October 30, 1989; accepted after revision January 30, 1990. This work was supported in part by fellowship J0283M (Erwin Schroedinger Stipendium), Austria, awarded to B. W. Schwaighofer. I Department of Radiology and Magnetic Resonance Institute, lkiiversity of Califomia, San Diego, Medical Center, 225 Dickinson St., San Diego. CA 92103-1990. Address reprint requests to D. J. Sarteds. 2 Present address: Department of Radiology, 2 Med. Univ. Klinik, Gamisongasse 13, A-1090 Vienna, Austria. 3 Department of RadiOlOgy, Lkiversity of California, San Diego, Medical Center, San Diego, CA 92103-1990. 4Department of Radiology. Veterans Administration Medical Center, 3350 La Jolla Village Dr., San Diego, CA 92161. 0361-803X/90/1 546-1 245 C American Roentgen Ray Society MR Imaging of the Temporomandibular Joint: A Cadaver Study of the Value of Coronal Images Recent studies comparing cryosectional anatomy of the temporomandibular joint (TMJ) to its MR appearance have shown that the assessment of disk displacement is inaccurate when based on the sagittal plane alone. This article describes the MR appearance of the normal and abnormal (positional and osseous changes) TMJ in the coronal plane and compares these findings with their cryosectional anatomy. Twentytwo TMJs from unselected frozen cadavers were embedded in paraffin. Coronal and sagittal MR imaging was performed; specimens were then cut in the same plane as the coronal images. Disk position by cryosection was normal in 14 cases and abnormal in eight cases. Coronal MR images alone correctly depicted the TMJ disk position in 17 cases (77%) (13 normal, four abnormal). Complementary sagittal images were necessary for diagnosing anterior displacement in two cases (9%). MR was inaccurate in three cases (14%) of severe degenerative joint disease. Bone condition was correctly diagnosed on the basis of coronal Images alone in all cases. Our study shows that coronal MR imaging alone of the TMJ in cadavers accurately shows disk position in 77% of cases. Complementary sagittal Images were of benefit In the diagnosis of an additional 9% with anterior displacement. Disk position was assessed inaccurately in either plane in patients with severe degenerative joint disease. For a full MR assessment of the TMJ for disk position and bone condition, we recommend imaging in both coronal and sagittal planes. AJR 154:1245-1249, June 1990 Pain and dysfunction of the temporomandibularjoint (TMJ) are a common clinical syndrome seen in up to 39% of the population [1 ]. Patients complaints include clicking, pain, crepitation, earache, and headache [2]. Potential causes are arthrosis, remodeling of the hard and soft structures, and internal derangements involving the articular disk and its attachments. Articular disk derangements frequently involve anterior [3, 4] and/or medial displacement [5, 6]. Different imaging techniques, including plain radiography, arthrography, and CT, were used to evaluate TMJ dysfunctions. Today, MR imaging has gained popularity among clinicians and radiologists with its ability to directly image disk margins and attachments. Sagittal MR imaging appears to be useful in the detection and delineation of disk configuration and displacement [2, 3, 7, 8]. The accuracy of MR imaging in assessing TMJ disk position has been found to be comparable with that of other imaging techniques, such as arthrography [9] and CT [8]. Recent studies comparing MR imaging with cryosectional anatomy have shown that the assessment of medial or lateral disk displacement based on the sagittal plane alone yields inaccurate results [4, 7, 9-1 2]. Additionally, rotational and sideways displacement of the disk frequently is misdiagnosed or missed entirely on sagittal MR imaging or arthrography [6]. Increased accuracy apparently can be achieved with MR by using a combination of sagittal and coronal views [6]. However, limitations of coronal plane MR imaging of both the normal and abnormal TMJ must be considered if it is routinely used to complement the sagittal images..
1246 SCHWAIGHOFER ET AL. AJR:154, June 1990 In this study, we describe the MR appearance of both the normal and abnormal TMJ in the coronal plane and compare these findings with their cryosectional anatomy. Positional derangements and bone abnormalities as seen in the coronal plane are described, and the diagnostic accuracy and limitations of MR imaging in the coronal plane alone and in combination with the sagittal plane are discussed. Materials and Methods Twenty-two TMJs in the closed-jaw position were removed as blocks measuring approximately 5 x 5 x 5 cm from unselected fresh deep-frozen cadavers. No information about age, sex, or possible clinical premorbid TMJ symptoms of the cadavers was available. Standardized positioning during MR imaging and cryosectioning was achieved by embedding the specimens in square blocks of paraffin with one side oriented parallel to the condylar long axis. Plain radiographs were used to confirm position. All scans were obtained on a commercially available Signa MR imager operating at 1.5 T (General Electric, Milwaukee, WI). Each specimen was thawed to room temperature and imaged with a 6.5- cm round planar surface coil operating in the receive mode. For best imaging quality, a special imaging protocol was used with an 8-cm field of view, 256 x 256 matrix, partial saturation pulse sequence with 600 msec repetition time and 20 msec echo time, and six excitations. Imaging was performed with 3-mm contiguous slices in the coronal plane (parallel to the long axis of the condyle) and a 3- mm slice thickness with a 1.5-mm interslice gap in the sagittal plane. The blocks were marked along these slices for sectioning. After MR imaging, the specimens were refrozen. Fine-tooth metalblade band saws and handsaws were used to cut each block in the same coronal plane as the coronal MR images. The cut surfaces of the specimens were photographed. The MR images were independently evaluated for disk position and bone abnormalities by three radiologists who had no knowledge of the cryosectional results. Once the coronal images of all specimens were reviewed, the sagittal images were examined for additional information not present on the coronal images. The sagittal images were not evaluated separately as there were no cryosections in this plane for comparison. If a consensus opinion was not initially achieved, the image(s) in question were reviewed again by all evaluators, and a final consensus diagnosis was then made. MR findings subsequently were correlated with cryosection observations (as the morphologic standard). The following criteria for disk position were used for both cryosections and MR images. The position of the TMJ disk was classified as normal or abnormal. If the disk was midway between the central portion of the condylar head and the apposing mandibular fossa, its position was considered normal [5, 1 1]. If the disk was displaced in either the coronal or sagittal plane, its position was considered to be abnormal. The position of an abnormal disk in the coronal plane was classified as either medial or lateral on the basis of its location relative to the superior surface of the condyle. Anterior displacement, if present, was diagnosed on the basis of the coronal MR image if the disk was seen on an image slice anterior to the condylar head and either no disk or only a small area of disk was noted above the condyle. Anterior disk displacement findings on coronal MR images then were correlated with the corresponding sagittal image. The cryosections and MR images of the TMJ joints were evaluated for evidence of osseous abnormalities, such as flattening and osteophytosis of the condyle, also. Results The results are summarized in Table 1. When compared with cryosectional anatomy, disk position was diagnosed correctly by coronal MR alone in 17 (77%) of the 22 joints and by the use of complementary coronal and sagittal MR images in 1 9 (86%) of the 22 joints. In 1 4 (64%) of the 22 cadaver specimens, cryosectional analysis showed the disk in a normal position. In 1 3 (93%) of these 14 cases, the disk position was diagnosed as normal on both coronal and sagittal MR images. On coronal MR images, normal disks were located superior to the condyle and had a homogeneous relatively low signal intensity that was readily distinguishable from the surrounding tissues (Fig. 1). Only one of the 14 cryosectional specimens with normal disk position had a disk that was not visible on MR. This specimen had severe degenerative changes of the condyle with marked disk thinning. No perforations were found on either cryosection or MR imaging. Abnormal disk position was noted on cryosection in eight (36%) of the 22 specimens. Seven cases had medially dislo- TABLE 1: Disk Position and Bone Abnormalities Diagnosed on the Basis of Cryosection and MR Images in 22 Patients Temporomandibular Condition Joint Cryosection Diagnosis Diagnosis by Coronal MR Images Only Diagnosis by Complementary Coronal and Sagittal MR Images Disk Position Normal 14 13 0 Abnormal displacement 8 4 2 Medial only 2 1 0 Lateral only 0 0 0 Anterior only 0 0 0 Anteromedial 5 3 2 Anterolateral 1 0 0 Bone Condition Normal 11 11 0 Abnormal 11 11 0 Osteoporosis 2 2 0 Degenerative changes 9 9 0
AJR:154, June 1990 MR OF TEMPOROMANDIBULAR JOINT 1247 Fig. 1.-A-C, Coronal schematic illustration (A), spin-echo Ti-weighted (600/20) MR image (B), and cryosection specimen (C) show normal right temporomandibular joint anatomy with disk positioned midway between central portion of condylar head and apposing mandibular fossa. CapeUle- - space - \, Lower jointspace Fig. 2.-A and B, Coronal spin-echo TIweighted (600/20) MR image (A) and cryosection specimen (B) show severe medial and mild anterior disk temporomandibular joint displacement. Marked medial displacement of disk (arrows) relative to medial pole of condyle is seen. Slight anterior displacement was evident on multiple coronal MR images and cryosection spedmens. cated disks; five also had anterior displacement. One specimen had anterolateral disk displacement. No specimens had isolated anterior or lateral disk displacement. MR images correctly depicted the position in all five specimens with anteromedial disk displacement (100%) (Fig. 2) and in one of two specimens with medial-only disk displacement (50%). MR images incorrectly depicted the TMJ disk position in the one specimen with anterolateral displacement (Fig. 3). The two specimens incorrectly diagnosed on the basis of MR findings A Lateral disc attachments- -_ Medial disc attachment had severe degenerative changes of the condyle with thinning of the disk (Fig. 3). Of the five specimens with anteromedial displacement diagnosed on the basis of MR findings, coronal views alone were sufficient for diagnosis of the anterior cornponent of the displacement in three cases, and the use of complementary sagittal images was necessary in two cases. MR images accurately correlated with the cryosections in the assessment of bone in all 22 cases (1 00%). The bone appeared normal in 1 1 of the 22 specimens.
1248 SCHWAIGHOFER ET AL. AJR:154, June 1990 Of the 1 1 specimens with bone abnormalities, two without degenerative changes had an accentuated trabecular bone pattern noted on both cryosectional examination and MA, which was interpreted as severe osteoporosis of the condyle. Nine specimens showed degenerative changes, including erosions, flattening, and osteophytosis of the condyle. The diagnosis of degenerative change was possible in all cases on the basis of coronal MR images alone. Erosions and flattening of the condyles, however, were better seen on coronal than on sagittal MR images (Fig. 4). Osteophytosis was better shown on sagittal than on coronal MR images. Discussion Our findings support previous studies showing that MR imaging clearly shows both normal [7, 1 1, 1 3] and abnormal TMJ position [7, 1 0, 13], except for cases involving severe degenerative joint disease. Coronal MR images alone allowed us to assess correctly the position of the TMJ disk in 77% of cases. The use of complementary sagittal MR images increased the accuracy to 86%. Our results correlate well with the only other published MR study that used both coronal and sagittal images [6], which revealed an accuracy of MR in the evaluation of disk position of 83% compared with cryosectional specimens. The inability of coronal views to provide additional information regarding disk position in a normal TMJ relative to the condylar head in our study is comparable to other reported results [8]. We found that inaccurate assessment of disk position by MR imaging occurred primarily in joints with severe degenerative changes involving a significantly thinned disk. For these cases, the joint spaces and surrounding tissues also had degenerative changes with an increase in MR signal intensity similar to that of the disk. Consequently, a distinct delineation of the thinned TMJ disk from surrounding tissue was not possible on MR. Several published reports discuss the occasional inability to differentiate the disk from the joint capsule, particularly in the presence of increased disk signal intensity resembling that of the capsule [9]. Fig. 3.-A and B, Coronal cryosection specimen (A) clearly shows anterolateral temporomandibular joint (TMJ) disk displacement (small arrows) on left side that was not diagnosed on the basis of coronal spin-echo Ti-weighted (600/20) MR images (B). Incorrect MR diagnosis of TMJ disk position occurred in the presence of severe condylar degenerative changes and bony erosions, which are seen on both MR image and cryosection (long arrows). Mediolateral displacements of the TMJ disk are not uncommon [6]; sideways displacement occurred in 36% of our specimens. The large percentage of patients with rotational anteromedial and medial sideways disk displacements supports recent findings that indicate that these derangements are more common than rotational anterolateral or lateral displacements [6]. Importantly, standard protocols that use only sagittal MR images are not sufficiently accurate in the evaluation of sideways TMJ disk displacement [6]. Consequently, a full MR examination of the TMJ for positional disk abnormalities would include imaging in both coronal and sagittal planes. Osseous abnormalities were diagnosed on all coronal images. The use of complementary sagittal MR images allowed better characterization of these changes. Coronal images more clearly depicted erosions and flattening of the condyles; sagittal images showed osteophytosis better. When sagittal MR imaging only is performed, accuracy in detecting the bone abnormalities may be as low as 60% [9]. Despite theoretical limitations of bone evaluation, MR has an accuracy rate in identifying osseous abnormalities (such as degenerative joint disease) comparable with that of CT [9], although these alterations may be less clearly visualized by MR [6]. Other reports suggest that CT remains superior in delineating osseous abnormalities [3, 8]. An important potential limitation of MR is its inability to reveal TMJ disk perforations, which are shown readily by arthrography [1 0, 14, 15]. Whereas an early study showed a TMJ disk perforation on sagittal Ti -weighted images [3], more recent reports suggest that disk or posterior attachment perforations may be missed by either sagittal or coronal MR imaging [9, 10]. The use of a cadavenc model could limit the direct application of our results to the clinical setting. Although the unselected specimens used in this study may not match the age and sex distribution of a typical clinical population, the accuracy of MR in characterizing pathologic changes present in the specimens should be comparable with that of in vivo MR imaging. The ability of MR to show early pathologic changes underscores the importance of distinguishing symp-
AJR:154, June 1990 MR OF TEMPOROMANDIBULAR JOINT 1249 Fig. 4.-A-C, Right coronal (A) and sagittal (B) spin-echo Ti-weighted (600/20) MR images and cryosection specimen (C) show condylar flattening and osteophytes. Cryosection specimen shows flattening and osteophytosis of condyle (long arrows) in addition to severe anteromedial disk displacement (arrowheads). Coronal image (A) shows condylar flattening (long arrows) better than sagittal image (B) does. Osteophytosis (short arrow) is shown more clearly on sagittal (B) than on coronal (A) image. tomatic anatomic change from asymptornatic pathologic change or normal variation. In the present study, the absence of information about premorbid clinical symptoms as related to the cryosectional findings makes the significance of the more subtle findings difficult to assess. Also, cadaveric joint specimens may have components that move during the thawing process, thus increasing the prevalence of both falsepositive and false-negative findings. The cadaveric model, however, provides an opportunity for accurate pathologic correlation that is unavailable in most clinical studies. Image quality of cadaver sections is maximized by the lack of movement and decreased noise from surrounding tissues. MR image quality in clinical studies may be degraded by patients movements, noise from surrounding tissue, and older ferromagnetic orthodontic appliances or surgical implants [3, 4, 12]. Additionally, incomplete imaging frequently occurs as the result of claustrophobic episodes [3, 4, 12]. In summary, the use of the coronal plane alone allows a good assessment of the TMJ disk position and bone condition, with additional information on anterior disk displacement provided by the complementary sagittal image. Inaccuracies also occur in the presence of severe degenerative joint disease. For an optimal study of this joint, we recommend the combined use of coronal and sagittal MR images. REFERENCES 1. Pullinger AG, Seligman DA, Solberg WK. Temporomandibular disorders. Part I: Functional status, dentomorphologic features, and sex difterences in a nonpatient population. J Prosth Dent i988;59:228-235 2. Sokoloft R, Sartoris DJ, Resnick D. uncovering the sources of temporomandibular jolnt malfunction. J Musculoskel Med 1988;5 :69-79 3. Harms SE, Wilk RM, Wolford LM, Chiles DG, Milan SB. The temporomandibular jolnt: magnetic resonance imaging using surface coils. Radiology 1985;157: 133-1 36 4. Harms SE, Wilk RM. Magnetic resonance imaging of the temporomandibular joint. RadioGraphics 1987;7 :521-542 5. Juniper RP. The pathogenesis and investigation of TMJ dysfunction. Br J Oral Maxillofac Surg 1987;25: 105-112 6. Katzberg RW, Westesson PL, Talents RH, et al. Temporomandibular joint: MR assessment of rotational and sideways disk displacement. Radiology 1988;169:741-748 7. Katzberg RW, Bessette RW, Talents RH, et al. Normal and abnormal temporomandibular joint: MR imaging with surface coil. Radiology 1986; 158: 183-1 89 8. Westesson P-L, Katzberg RW, Talents RH, Sanchez-Woodworth RE, Svensson SA. CT and MR of the temporomandibular joint: comparison with autopsy specimens. AJR 1987:148:1165-1171 9. Westesson P-L, Katzberg RW, Talents RH, Sanchez-Woodworth RE, Svensson SA, Espeland MA. Temporomandibular joint: comparison of MR images with cryosectional anatomy. Radiology 1987;164:59-64 10. Donlon WC, Moon KL. Comparison of magnetic resonance imaging, arthrotomograph and clinical and surgical findings in temporomandibular joint derangements. Oral Surg Oral Med Oral Pathol 1987;64:2-5 1 1. Kaplan PA, Tu HK, Williams SM, Lydiatt DD. The normal temporomandibular joint: MR and arthrographic correlation. Radiology 1987;1 65:177-178 12. Schellhas KP, Wilkes CH, Fritts HM, Omlie MR. Heithoft KB, Jahn JA. Temporomandibularjoint: MR imaging of internal derangements and postoperative changes. AJR 1988:150:381-389 13. Roberts D, Schenck J, Joseph P. et al. Temporomandibularjoint: magnetic resonance imaging. Radiology 1985:155:829-830 14. Westesson P-L, Bronstein SL, Uedberg J. Temporornandibular joint: ocrrelation between single-contrast videoarthrography and postmortem morphology. Radiology 1986:160:767-771 15. Westesson P-L, Rohlin M. Diagnostic accuracy of double-contrast arthrotomography of the temporomandibular joint: correlation with postmortem morphology. AiR 1984:5:463-468